42 



BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



of the fertilization of Pima flowers by Pima pollen and by pollen of 

 a very different but still compatible type of cotton (upland), shows 

 that in several cases somewhat better fertilization resulted from the 

 foreign pollen. This is of especial interest in view of the fact that 

 the pistils of the upland varieties used in these experiments (Acala 

 and Lone Star) are much shorter than the Pima pistils. 



RAPIDITY OF GERMINATION AND DEVELOPMENT OF DIFFERENT POLLENS. 



Comparison of like and unlike pollens in respect to the rapidity 

 of development of the tubes was the object of an experiment per- 

 formed in 1920. Pima flower buds were emasculated in the evening 

 and were thoroughly cross-pollinated the following day, some with 

 pollen from other Pima plants, others with pollen ot Acala (up- 

 land). The pistils were then excised at the summit of the ovary at 

 successive intervals of time. 



Table 24. — Comparison of the rapidity of germination and development of dif- 

 ferent pollens, as shoicn oy Pima flowers tcith pistils excised at successive 

 intervals of time after pollination. 



Pistil excision. 



Pollination with Pima 

 (Egyptian) pollen. 



Pollination with Acala 

 (upland) pollen. 



Hour excised. 



After i Percent- 



pollina- i Flowers ; age of 



tion treated. ! bolls 



(hours). | matured. 



Mean 





Percent- 



number of 



Flowers 



age of 



seeds per 



treated. 



bolls 



boll. 





matured. 



13.7±1.4 



37 







11. 5± .6 



35 



45.7±5.7 



13. 5± .6 



35 



51.5±5.7 



15. 7± .6 



34 



73.5±5.1 



15. 6± .5 



39 



95. 0±2. 4 



14. 4± .5 



25 



84.0±4.9 



Mean 

 number of 



bo 



sper 



8p.m. 

 5 a.m. 

 7 a.m. 

 9 a.m. 

 11 a. m 

 1 p. m. 



16* 

 18J 



22* 

 24* 



40 ! 

 39 

 35 

 36 I 



35 I 

 26 i 



i 



7.5±2.8 

 61.5±5.2 j 

 63.0±5.5 ! 

 91.8±3.0 i 

 80.0±4.6 i 

 92. 3 ±3. 5 ! 







13.7±0.8 

 14.5±1.0 

 15. 6± .6 

 15. 0± .4 

 14. 5± .7 



The data of this experiment, as given in Table 24, indicate that 

 the Pima and the upland pollen were equally efficient in fertilizing 

 the Pima flowers. There was also no important difference between 

 the two pollens in the rate of growth of the tubes, as indicated by 

 the degrees of fertilization at successive intervals after pollination, 

 except that of the flowers excised 7§ hours after pollination, three 

 which had been pollinated with Pima pollen set bolls, while no bolls 

 developed from flowers pollinated with Acala pollen which had been 

 excised at this early hour. 



POLLEN COMPETITION AS A FACTOR IN SELF-FERTILIZATION 

 AND CROSS-FERTILIZATION. 



Evidence was given on a preceding page that when the several 

 pollens were applied separately to the Pima stigmas, approximately 

 equal compatibility of self pollen, pollen from other plants of the 

 same variety, pollen of another Egyptian variety, and pollen of an- 

 other type of cotton (upland) was shown by the degree of fertiliza- 

 tion effected. Fairly satisfactory evidence also was presented that 

 the tubes of Pima and of upland pollen grow with approximately 

 equal rapidity when these pollens are applied separately. It remains 

 to consider whether, when different pollens are in competition on the 

 stigmas of the same flower, selective fertilization occurs. 



